12 farmers' bulletin 831. 



Some have stated that infestation spreads through a field only by- 

 means of the interlacing cotton branches, and that by increasing the 

 spacing tlie spread of the red spider can be prevented. Since it is 

 now known, however, that the mites commonly travel on the ground 

 also, from plant to plant, it is easily seen that wide spacing of cotton 

 plants will by no means entirely prevent the spread of the pest. 



MAINTAINING MULCH. 



By maintaining continually in fields a finely pulverized surface 

 mulch the progress of migrating mites is somewhat retarded and th6 

 development of infestation correspondingly discouraged. The plant- 

 ing of cotton by the checking system permits the cultivation of each 

 plant on four sides and is a good method from the viewpoint of the 

 control of the red spider. 



ROTATION. 



Since the wild grasses and small grains appear to be about the only 

 plants which are free from red-spider attack, there are few immune 

 crops which can be used for the purpose of rotation. Furthermore, 

 provided the sources of infestation were allowed to remain, the pest 

 would surely reinvade fields, upon the return to cotton, even should 

 the small grains or grasses be planted for a time. 



Although the fertilizhig of cotton land in no way discourages the 

 development of red spiders, yet the judicious use of fertilizei-s in- 

 vigorates the plants so that they are better fitted to overcome the 

 injury. 



REPRESSIVE MEASURES. 



Under the heading "Repressive measures" may be discussed those 

 measures which can be taken to combat the pest when it has gained 

 entrance to cotton fields. It has been demonstrated that it is possible 

 to eradicate the pest from infested fields. 



By keeping a constant watch of cotton fields the earliest affected 

 stalks may be detected and destroyed. In using this method it 

 usually is necessary to repeat the operation several times, since certain 

 plants are likely to be overlooked during the first inspection. Great 

 care should be taken to locate every plant which shows infestation, 

 and these must be taken from the field, without brushing against 

 healthy plants, and burned immediately. If infestation has not ad- 

 vanced too far, the prompt application of this method usually is 

 effective. 



. If infestation has spread until a considerable patch has become 

 involved, more drastic steps are necessary than those just mentioned. 



